The invention relates to devices for propagating magnetic domains. Such devices each include a monocrystalline nonmagnetic substrate bearing a layer of an iron garnet capable of supporting local enclosed magnetic domains. The iron garnet layer has a stress-induced uniaxial magnetic anisotropy component. The stress is caused by growing the layer in compression on the nonmagnetic substrate. The iron-garnet is of the class of iron garnet materials with positive magnetostriction constants.
In magnetic "bubble" domain devices, the smaller the bubble diameter, the larger the information storage density which can be achieved. Iron garnet bubble domain materials are preferred in bubble domain technology because small diameter bubble domains are stable in these materials. For a bubble domain material to be useful for use in bubble domain devices, it is also important that the bubbles formed in the material should have a high wall mobility so that comparatively small driving fields can cause rapid bubble movement. This property enables one to operate the device at high frequencies and at low energy dissipation.
It is also important that the magnetic bubble domain material should have a high uniaxial anisotropy. This is necessary in order to avoid spontaneous nucleation of bubbles. This is of great importance for reliable information storage and processing within the bubble domain material.
The overall uniaxial anisotropy (K.sub.u) may have contributions of stress-induced (K.sub.u.sup.s) and growth-induced (K.sub.u.sup.g) components. This means that EQU K.sub.u .apprxeq.K.sub.u.sup.s +K.sub.u.sup.g. (1)
In a bubble domain material known from German Offenlegungsschrift No. 2,232,902, K.sub.u is mainly determined by the stress-induced component. This known bubble domain material is obtained by depositing a single crystal iron garnet film having a selected crystallographic orientation and having a positive magnetostriction constant, on a substrate. The lattice constant of the film is larger than the lattice constant of the substrate. When such a film having a positive magnetostriction constant is placed under a compressive stress, the magnetostriction contribution to the magnetic anisotropy tends to produce an easy axis of magnetization perpendicular to the plane of the film.
The bubble domain material which resulted from the above concept was a (111) oriented film of Tb.sub.3 Fe.sub.5 O.sub.12 which had been deposited on a Sm.sub.3 Ga.sub.5 O.sub.12 substrate. The value of the required positive magnetostriction constant was determined by the choice of the rare-earth ion in the bubble domain material, and the amount of compressive stress was determined by the choice of the substrate.
This concept does not lead to a bubble domain material which is suitable for propagating therein bubble domains having a diameter smaller than 1 .mu.m, while using comparatively low driving fields (for which purpose a high K.sub.u and a high wall mobility are required) and which can also be deposited on a Gd.sub.3 Ga.sub.5 O.sub.12 substrate. As a matter of fact, to achieve a high K.sub.u by the incorporation of rare-earth ions having a high positive magnetostriction constant inevitably leads to the use of Sm and Eu ions, which provide considerable, undesireable damping. On the other hand a high K.sub.u can be achieved to only a limited extent by increasing the compression of the film. This is because when the compression becomes too large, it disappears and the film comes under a tensile stress. Moreover, this would require the use of substrate materials other than Gd.sub.3 Ga.sub.5 O.sub.12 (lattice parameter 12.376).